I. Field of the Invention
This invention relates to a moisture (water) analyzer, or apparatus for the detection, and measurement of moisture in fluid streams. In particular, it relates to apparatus for the detection, and continuous accurate measurement of moisture in small and infinitesmal, or trace concentrations in flowing gas streams.
II. Background and Prior Art
Industrial operations often require the detection, and continuous accurate measurement of moisture in process streams, e.g., hydrocarbon streams. In natural gas production, for example, the gas contains many constituents other than gaseous hydrocarbons. Many are undesirable contaminants, e.g., glycols, methanolamine, iron oxide particulates (rouge), and methanol antifreeze which is often injected into natural gas lines. Water is one of the most abundant of the constituents of natural gas, and it is often present as liquid droplets, or in vapor form, or both. Water in condensed form can generally be removed by mechanical means. Water in vapor form, however, is not so easily removed. Consequently, in many operations, it is necessary to continuously and accurately measure the amount of water vapor present in gas; even when the moisture is present only in trace amounts, or concentrations measured in parts per million (ppm), based on the total volume (or weight) of the gas. Pipeline and natural gas distribution companies, e.g., expect relatively dry gas to be delivered into their distribution systems. Wet gas can cause many operating problems; not the least of which is that the gas distributor may be required to pay for water vapor left in the gas stream. It is therefore important to this industry, and to many other industries, that the moisture content of the gas be accurately detected, and measured at the point of delivery to pipeline or gas distribution systems.
Various apparatus and methods are known for the measurement of water in gases. Some utilize electrolytic sensors; some measure dew point by optical means; some utilize a vibrating crystal; some are capacitance and impedance detectors; and some simply use wet chemical measurement techniques. In U.S. Pat. No. 2,830,945 to F. E Keidel there is described an instrument or apparatus, which utilizes an electrolytic sensor for the determination, and measurement of the amount of moisture in gases. The analysis is carried out in a special cell which combines water absorption with electrolysis. An absorbent, electrically conductive when wet, is dispersed as a thin viscous film of hydroscopic electrolyte within a Teflon tube in contact with two platinum electrodes, constituting a portion of an external electrical circuit. Moisture in the gas flowing through the cell is absorbed by the hydroscopic film, a partially hydrated phosphorus pentoxide, the water being electrolyzed to oxygen and hydrogen. The absorbed water is quantitatively electrolyzed at the electrodes by the application of a dc voltage greater than the decomposition potential of the water. The current produced in the external circuit is directly proportional to the water content of the gas and serves as a direct measurement of the water content of the gas.
Whereas the apparatus of Keidel and those of others have been used with varying degrees of success, none are ideal. Some of these instruments are not specific to water such that contaminants interfere with proper operation of the instrument. Some are dependent on the flow rate of the stream being measured, and often the sensor is easily damaged by contaminant liquids and solids. The instrument becomes unresponsive, and recovery slow after the instrument is slugged by water.